Human females and other primates experience what is referred to as a “period” as part of the reproductive, or menstrual, cycle. This is the phase of their cycle when the lining of the uterus, which has engorged with blood and becomes thicker in preparation for receipt of a fertilized egg, sloughs off in the absence of a fertilized egg, resulting in the release of blood. Do dogs experience the same cycle?
Pet parents may notice blood and discharge from their unspayed female dog’s vagina and may think their dog is having a period, much the same as humans do. Actually, this is not the case. Dogs do not have periods as such, they have heat, or ‘estrus’ cycles. The blood that is released during your dog's estrus cycle is part of a different process than that which occurs in humans. In female dogs, the genitals and reproductive organs become supplied with extra blood in preparation for breeding, and some bleeding may result. This is different than the process in humans, when bleeding is a result of successful breeding not taking place. So while both humans and dogs experience blood discharges which may seem similar, and are related to the respective female's reproductive cycle, they are, in fact, not the same. Dogs do not have periods like humans do.
Dogs do not have periods, they have estrus cycles, commonly referred to as coming into heat. Estrus, in an unspayed female dog, occurs once or twice a year. While humans go through estrus every 28 days, dogs’ cycles usually take approximately 180 days. When female dogs experience estrus they are receptive to the male dog for mating--female dogs are not receptive to mating when they are not experiencing heat. While dogs are in heat, there may be some bloody discharge from your dog's vagina, due to engorgement of the genitals with blood in preparation for mating and fertilization. This is not the same as menstruation, which is the release or absorption of the uterine lining in a female mammal. If mating and fertilization do not occur in a female dog, the nutrient-rich lining of the uterus which has thickened in preparation for fertilization is absorbed back into the dog, not released. This is referred to a covert menstruation.
So, while bloody discharge from the vagina in humans marks the end of the reproductive cycle, in dogs, it marks their fertile time.
In dogs, the estrus cycle consists of four phases:
- Proestrus: 3 - 17 days, characterized by production of estrogen, bloody vaginal discharge, body prepares for mating and fertilization
- Estrus: 4-7 days, luteinizing hormone is released, bleeding may continue, although it may decrease, female is receptive to mating, ovulation occurs
- Diestrus: lasts about 6 days, discharge ceases, if not pregnant the uterine lining is absorbed back into the female dog's body
- Anestrus: the final 2-3 month span of your dog's estrous cycle, when your dog is not hormonally active or sexually receptive
The amount of blood discharge from a female dog during their heat cycle varies between individuals, with some leaving a blood trail all over your house, and some producing such negligible blood that it is not noticeable.
If you have an unspayed female and are not planning on using her as part of a reputable breeding program, spaying your dog will prevent her going through her estrous cycle, and unwanted symptoms that occur in conjunction with heat cycles, such as bloody discharge from the vagina. In addition, spaying will prevent unwanted puppies. With the number of stray and shelter dogs available, producing puppies that are not part of a breeding program is not recommended.
Spaying can be performed by your veterinarian by either an ovariectomy, the removal of the ovaries, or an ovariohysterectomy, the removal of ovaries, uterus, and cervix. Both procedures will prevent unwanted pregnancy and heat cycles.
Dogs and humans all experience estrus, that is, a time when an ovum is released and they are fertile and can become pregnant.
- The uterus lining engorges and prepares for implantation and nourishment of an embryo during this time.
- Hormones are produced and an egg is released; estrogen, ovulation, luteinizing hormone and post estrus are similar in mammals.
While all mammals have an estrous cycle, how the cycle progresses differs amongst different species.
- Humans experience a monthly estrus cycle versus dogs, which experience estrus approximately twice a year.
- In dogs, the uterine lining is absorbed if pregnancy does not result, whereas in humans it is not absorbed but shed and released, resulting in a “period”, or menstruation.
- Humans are sexually receptive regardless of the phase of estrous they are experiencing. Dogs and most other female mammals are only receptive during their heat or estrus phases.
The pet parent of a young female dog means to have her spayed but, due to several incidents in her personal and professional life, is unable to arrange the procedure at the recommended six months of age. As a few weeks turn into months, her young dog begins experiencing a heat cycle. With the unwanted heat cycle comes a bloody discharge that leaves a rather noticeable mess all over the pet parent’s white carpet and home.
Although spay can be conducted during a heat cycle, there are more complications possible, so the pet parent decides to restrict her dog’s access to other dogs during the heat cycle so she does not become pregnant, discards the white carpet, cleans up for the several days of the heat cycle, and arranges for a spay after her dog’s cycle is complete so this does not happen again! After her dog’s spay there are no more messy heat cycles.